Catalyst system and its use for the polymerization of propylene

ABSTRACT

A catalyst system which can be used in the polymerization of propylene comprises at least one metallocene as a rac/meso isomer mixture, at least one organoboroaluminum compound, at least one passivated support, at least one Lewis base and, if desired, at least one further organometallic compound.

The present invention relates to catalyst systems and their use in thepolymerization of propylene.

Processes for preparing polyolefins with the aid of soluble, homogeneouscatalyst systems comprising a transition metal component of themetallocene type and a cocatalyst component such as an aluminoxane, aLewis acid or an ionic compound are known. These catalysts have a highactivity and give polymers and copolymers having a narrow molar massdistribution.

In polymerization processes using soluble, homogeneous catalyst systems,thick deposits are formed on reactor walls and stirrers if the polymeris obtained as a solid. These deposits are formed by agglomeration ofpolymer particles whenever metallocene and/or cocatalysts are present indissolved form in the suspension. Such deposits in the reactor systemshave to be removed regularly since they quickly attain considerablethicknesses, have a high strength and prevent heat transfer to thecooling medium. Such homogeneous catalyst systems cannot be used inmodern industrial polymerization processes in the liquid monomer or inthe gas phase.

To avoid deposit formation in the reactor, it has been proposed thatsupported catalyst systems in which the metallocene and/or the aluminumcompounds serving as cocatalyst are immobilized on an inorganic supportmaterial be used.

EP-A-0,576,970 discloses metallocenes and corresponding supportedcatalyst systems.

Highly active supported catalyst systems for preparing industriallyimportant polyolefins having high tacticity and a high melting point, inparticular polypropylenes, comprise ansa-metallocenes in racemic orpseudoracemic form and are known, for example, from EP-A-0,530,647;EP-A-0,576,970 and EP-A-0,653,433.

Ansa-Metallocenes are obtained in the synthesis as isomer mixtures (racform and meso form or pseudo rac/pseudo meso form), so that anadditional and complicated process step for separating rac and mesoforms (or the pseudo forms) is necessary. A definition of the terms racform and meso form may be found in Brinzinger et al., Journal ofOrganometallic Chemistry, 232 (1982) page 233 and Schlögl, Top.Stereochem., 1 (1967) page 39 ff.

In addition, methylaluminoxane (MAO) as hitherto the most effectivecocatalyst has the disadvantage of having to be used in a large excess.Such aluminoxanes are described, for example, in JACS 117 (1995),6465-74, Organometallics 13 (1994), 2957-2969.

The preparation of cationic alkyl complexes opens a route to MAO-freecatalysts having comparable activity in which the cocatalyst can be usedin a virtually stochiometric amount.

Industrial utilization of metallocene catalysts necessitates, asdescribed above, their conversion into a heterogeneous catalyst systemin order to ensure an appropriate morphology of the resulting polymer.The application of cationic metallocene catalysts based on borate anionsto supports is described in WO-91/09882. Here, the catalyst system isformed by application of a dialkyl-metallocene compound and aBrönsted-acid, quaternary ammonium compound having a noncoordinatinganion such as tetrakispentafluorophenylborate to an inorganic support.The support material is modified beforehand using a trialkylaluminumcompound. A disadvantage of this process for application to a support isthat only a small part of the metallocene used is immobilized byphysisorbtion on the support material. When the catalyst system isintroduced into the reactor, the metallocene can easily be leached fromthe support surface. This leads to a polymerization which occurs partlyhomogeneously, resulting in an unsatisfactory morphology of the polymer.

It is an object of the present invention to find an inexpensive, highlyactive catalyst system for the preparation of polypropylene having hightacticity and a high melting point and also to provide a simple andeconomical process for preparing such a catalyst system, which processrequires no additional separation of rac and meso forms of themetallocene components present and does not use aluminoxanes such asmethylaluminoxane (MAO) as cocatalyst.

We have found that this object is achieved by a catalyst systemcomprising at least one metallocene as rac/meso isomer mixture, at leastone organoboroaluminum compound, at least one passivated support, atleast one Lewis base and, if desired, at least one furtherorganometallic compound.

The present invention accordingly provides a catalyst system comprising

a) at least one substituted metallocene of the formula A

 where

R¹ and R² are identical or different and are each a hydrogen atom, aC₁-C₂₀-hydrocarbon group such as a C₁-C₂₀-alkyl group, preferablymethyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl,tert-butyl, pentyl or hexyl, a C₆-C₁₄-aryl group or a C₂-C₂₀-alkenylgroup, with the proviso that R¹ is not methyl when R² is hydrogen,

M¹ is a transition metal of group 4, 5 or 6 of the Periodic Table of theElements, for example titanium, zirconium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum or tungsten, preferably titanium,zirconium or hafnium, particularly preferably zirconium,

A is a bridge of the formula

 or ═BR³, AIR³, —S—, —SO—, —SO₂—, ═NR³, ═PR³, ═P(O)R³, o-phenylene,2,2′-biphenylene, where

M² is carbon, silicon, germanium, tin, nitrogen or phosphorus,preferably carbon, silicon or germanium, in particular carbon orsilicon,

o is 1, 2, 3 or 4, preferably 1 or 2,

R³ and R⁴ are identical or different and are each, independently of oneanother, a hydrogen atom, halogen, a C₁-C₂₀ group such as C₁-C₂₀-alkyl,in particular a methyl group, C₆-C₁₄-aryl, in particular a phenyl ornaphthyl group, C₁-C₁₀-alkoxy, C₂-C₁₀-alkenyl, C₇-C₂₀-arylalkyl,C₇-C₂₀-alkylaryl, C₆-C₁₀-aryloxy, C₁-C₁₀-fluoroalkyl, C₆-C₁₀-haloaryl,C₂-C₁₀-alkynyl, C₃-C₂₀-alkylsilyl, for example trimethylsilyl,triethylsilyl or tert-butyldimethylsilyl, C₃-C₂₀-arylsilyl, for exampletriphenylsilyl, or C₃-C₂₀-alkylarylsilyl, for exampledimethylphenylsilyl, diphenylsilyl or diphenyl-tert-butylsilyl, or R³and R⁴ may together form a monocyclic or polycyclic ring system, and

A is preferably dimethylsilanediyl, dimethylgermanediyl, ethylidene,methylethylidene, 1,1-dimethylethylidene, 1,2-dimethylethylidene,tetramethylethylidene, isopropylidene, phenylmethylmethylidene,diphenylmethylidene, particularly preferably dimethylsilanediyl,dimethylgermanediyl or ethylidene,

X are identical or different and are each a hydrogen atom, a halogenatom such as fluorine, chlorine, bromine or iodine, a hydroxyl group, aC₁-C₁₀-alkyl group such as methyl, ethyl, propyl, isopropyl, n-butyl,isobutyl, sec-butyl, tert-butyl, hexyl or cyclohexyl, a C₆-C₁₅-arylgroup such as phenyl or naphthyl, a C₁-C₁₀-alkoxy group such as methoxy,ethoxy or tert-butoxy, a C₆-C₁₅-aryloxy group, a benzyl group, an NR⁵ ₂group, where R⁵ are identical or different and are each a C₁-C₁₀-alkylgroup, in particular methyl and/or ethyl, a C₆-C₁₅-aryl group, a(CH₃)₃Si group, preferably a chlorine atom, a fluorine atom, a methylgroup, a benzyl group or an NMe₂ group, particularly preferably achlorine atom or a methyl group,

where the ratio of rac isomer to meso isomer of the metallocene of theformula (A) in the novel catalyst system is from 1:10 to 2:1, preferablyfrom 1:2 to 3:2,

b) at least one Lewis base of the formula I,

M³R⁶R⁷R⁸  (I)

 where

R⁶, R⁷ and R⁸ are identical or different and are each a hydrogen atom, aC₁-C₂₀-alkyl group, a C₁-C₂₀-haloalkyl group, a C₆-C₄₀-aryl group, aC₆-C₄₀-haloaryl group, a C₇-C₄₀-alkylaryl group or a C₇-C₄₀-arylalkylgroup, where two radicals or all three radicals R⁶, R⁷ and R⁸ may bejoined to one another via C₂-C₂₀ units and M³ is an element of maingroup V of the Periodic Table of the Elements,

c) a support,

d) at least one organoboroaluminum compound which is made up of units ofthe formula II

R_(i) ⁹M⁴—O—M⁴R_(j) ¹⁰  (II)

 where

R⁹ and R¹⁰ are identical or different and are each a hydrogen atom, ahalogen atom, a C₁-C₄₀ group, in particular C₁-C₂₀-alkyl,C₁-C₂₀-haloalkyl, C₁-C₁₀-alkoxy, C₆-C₂₀-aryl, C₆-C₂₀-haloaryl,C₆-C₂₀-aryloxy, C₇-C₄₀-arylalkyl, C₇-C₄₀-haloarylalkyl, C₇-C₄₀-alkylarylor C₇-C₄₀-haloalkylaryl, or R⁹ may be an —OSiR₃ group, where R areidentical or different and are as defined for R⁹,

M⁴ are identical or different and are each an element of main group 3 ofthe Periodic Table of the Elements and

i and j are each an integer 0, 1 or 2,

and is covalently bound to the support,

and, if desired,

e) an organometallic compound of the formula V

[M⁵R¹¹ _(p)]_(k)  (V)

 where

M⁵ is an element of main group I, II or III of the Periodic Table of theElements,

R¹¹ are identical or different and are each a hydrogen atom, a halogenatom or a C₁-C₄₀ group, in particular a C₁-C₂₀-alkyl group, aC₆-C₄₀-aryl group, a C₇-C₄₀-arylalkyl group or a C₇-C₄₀-alkylaryl group,

p is an integer from 1 to 3 and

k is an integer from 1 to 4.

The Lewis bases of the formula (I) are preferably ones in which M³ isnitrogen or phosphorus. Examples of such compounds are triethylamine,triisopropylamine, triisobutylamine, tri(n-butyl)amine,N,N-dimethylaniline, N,N-diethylaniline, N,N-2,4,6-pentamethylaniline,dicyclohexylamine, pyridine, pyrazine, triphenylphosphine,tri(methylphenyl)phosphine and tri(dimethylphenyl)phosphine.

The support component of the catalyst system of the present inventioncan be any organic or inorganic, inert solid, in particular a poroussupport such as talc, inorganic oxides and finely divided polymerpowders (e.g. polyolefins).

Suitable inorgainc oxides may be found among the oxides of elements ofgroups 2,3,4,5,13,14,15 and 16 of the Periodic Table of the Elements.Examples of oxides preferred as support include silicon dioxide,aluminum oxide and mixed oxides of the two elements and correspondingoxide mixtures. Other inorganic oxides, which may be used either aloneor in combination with the abovementioned preferred oxidic supports, arefor example, MgO, ZrO₂ , TiO₂ or B₂O₃, to name only a few.

The support materials used have a specific surface area in the rangefrom 10 to 1000 m²/g, a pore volume in the range from 0.1 to 5 ml/g anda mean particle size of from 1 to 500 μm. Preference is given tosupports having a specific surface area in the range from 50 to 500 μm,a pore volume in the range from 0.5 to 3.5 ml/g and a mean particle sizein the range from 5 to 350 μm. Particular preference is given tosupports having a specific surface area in the range from 200 to 400m²/g, a pore volume in the range from 0.8 to 3.0 ml/g and a meanparticle size of from 10 to 200 μm.

If the support material used naturally has a low moisture content orresidual solvent content, dehydration or drying prior to use can beomitted. If this is not the case, for example when using silica gel assupport material, dehydration or drying is advisable. Thermaldehydration or drying of the support material can be carried out underreduced pressure with simultaneous inert gas blanketing (e.g. nitrogen).The drying temperature is in the range from 100 to 1000° C., preferablyfrom 200 to 800° C. In this case, the parameter pressure is notcritical. The duration of the drying process can be from 1 to 24 hours.Shorter or longer drying times are possible, provided that equilibriumwith the hydroxyl groups on the support surface can be established underthe conditions selected, which normally takes from 4 to 8 hours.

Dehydration or drying of the support material can also be carried out bychemical means by reacting the absorbed water and the hydroxyl groups onthe surface with suitable passivating agents. The reaction with thepassivating reagent can convert all or some of the hydroxyl groups intoa form which leads to no adverse interaction with the catalyticallyactive centers. Suitable passivating agents are, for example, siliconhalides and silanes, e.g. silicon tetrachloride, chlorotrimethylsilane,dimethylaminotrichlorosilane, or organometallic compounds of aluminum,boron and magnesium, for example trimethylaluminum, triethylaluminum,triisobutylaluminum, triethylborane, dibutylmagnesium. Chemicaldehydration or passivation of the support material is carried out, forexample, by reacting a suspension of the support material in a suitablesolvent in the absence of air and moisture with the passivating reagentin pure form or as a solution in a suitable solvent. Suitable solventsare, for example, aliphatic or aromatic hydrocarbons such as pentane,hexane, heptane, toluene or xylene. Passivation is carried out at from25° C. to 120° C., preferably from 50 to 70° C. Higher and lowertemperatures are possible. The reaction time is from 30 minutes to 20hours, preferably from 1 to 5 hours. After chemical dehydration iscomplete, the support material is isolated by filtration under inertconditions, washed one or more times with suitable inert solvents ashave been described above and subsequently dried in a stream of inertgas or under reduced pressure.

Organic support materials such as finely divided polyolefin powders(e.g. polyethylene, polypropylene or polystyrene) can also be used andshould likewise be freed of adhering moisture, solvent residues or otherimpurities by means of appropriate purification and drying operationsprior to use.

The catalyst system of the present invention comprises, ascocatalytically active chemical compound, at least oneorganoboroaluminum compound comprising units of the formula (II).Preference is given to compounds of the formula (II) in which M³ isboron or aluminum.

The compound comprising units of the formula (II) may be in the form ofa monomer or a linear, cyclic or cage-like oligomer. It is also possiblefor two or more chemical compounds comprising units of the formula (II)to form dimers, trimers or higher associates with one another by meansof Lewis acid-Lewis base interactions or condensation reactions. It isalso possible to use mixtures of the compounds described.

Preferred cocatalytically active organoboroaluminum compounds d)correspond to the formulae (III) and (IV),

where R⁹ and R¹⁰ are as defined under formula (II).

Examples of cocatalytically active compounds of the formulae (III) and(IV) are

The organometallic compounds of the formula (IV) are preferablyuncharged Lewis acids in which M⁵ is lithium, magnesium and/or aluminum,in particular aluminum.

Examples of preferred organometallic compounds of the formula (V) aretrimethylaluminum, triethylaluminum, triisopropylaluminum,trihexylaluminum, trioctylaluminum, tri-n-butylaluminum,tri-n-propylaluminum, triisoprenaluminum, dimethylaluminum monochloride,diethylaluminum monochloride, diisobutylaluminum monochloride,methylaluminum sesquichloride, ethylaluminum sesquichloride,dimethylaluminum hydride, diethylaluminum hydride, diisopropylaluminumhydride, dimethylaluminum trimethylsiloxide, dimethylaluminumtriethylsiloxide, phenylalane, pentafluorophenylalane and o-tolylalane.

The metallocene of the formula (A) is preferably one of the followingcompounds:

dimethylsilanediylbis(2-methyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-tert-butylphenyl)indenyl)hafniumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-tert-butylphenyl)indenyl)titaniumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-methylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-ethylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-n-propylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-isopropylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-n-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-hexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-sec-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-phenyl)indenyl)zirconium dichloride

dimethylsilanediylbis(2-ethyl-4-(4′-methylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-ethylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-n-propylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-isopropylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-n-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-hexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-pentylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-cyclohexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-sec-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-phenyl)indenyl)zirconium dichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-methylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-ethylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-n-propylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-isopropylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-n-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-hexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-cyclohexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-sec-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-propyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-phenyl)indenyl)zirconium dichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-methylphenyl) indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-ethylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-n-propylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-isopropylphenyl) indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-n-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-hexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-cyclohexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-sec-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-n-butyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-hexyl-4-phenyl)indenyl)zirconium dichloride

dimethylsilanediylbis(2-hexyl-4-(4′-methylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-hexyl-4-(4′-ethylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-hexyl-4-(4′-n-propylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-hexyl-4-(4′-isopropylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-hexyl-4-(4′-n-butylphenyl)zirconium dichloride

dimethylsilanediylbis(2-hexyl-4-(4′-hexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-hexyl-4-(4′-cyclohexylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-hexyl-4-(4′-sec-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-hexyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

dimethylsilanediylbis(2-methyl-4-(4′-tert-butylphenyl)indenyl)zirconiumbis(dimethylamide)

dimethylsilanediylbis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)dibenzylzirconium

dimethylsilanediylbis(2-methyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium

imethylgermanediylbis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

dimethylgermanediylbis(2-ethyl-4-(4′-tert-butylphenyl)indenyl) hafniumdichloride

dimethylgermanediylbis(2-propyl-4-(4′-tert-butylphenyl)indenyl)titaniumdichloride

dimethylgermanediylbis(2-methyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

ethylidenebis(2-ethyl-4-phenyl)indenyl)zirconium dichloride

ethylidenebis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

ethylidenebis(2-n-propyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

ethylidenebis(2-n-butyl-4-(4′-tert-butylphenyl)indenyl)titaniumdichloride

ethylidenebis(2-hexyl-4-(4′-tert-butylphenyl)indenyl)dibenzylzirconium

ethylidenebis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)dibenzylhafnium

ethylidenebis(2-methyl-4-(4′-tert-butylphenyl)indenyl)dibenzyltitanium

ethylidenebis(2-methyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

ethylidenebis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)dimethylhafnium

ethylidenebis(2-n-propyl-4-phenyl)indenyl)dimethyltitanium

ethylidenebis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)zirconiumbis(dimethylamide)

ethylidenebis(2-ethyl-4-(4′-tert-butylphenyl)indenyl) hafniumbis(dimethylamide)

ethylidenebis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)titaniumbis(dimethylamide)

methylethylidenebis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

methylethylidenebis(2-ethyl-4-(4′-tert-butylphenyl) indenyl)hafniumdichloride

phenylphosphinediyl(2-ethyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride

phenylphosphinediyl(2-methyl-4-(4′-tert-butylphenyl)indenyl) zirconiumdichloride

phenylphosphinediyl(2-ethyl-4-(4′-tert-butylphenyl)indenyl) zirconiumdichloride

Further examples of metallocenes which can be used according to thepresent invention are analogues of the above metallocenes in which thezirconium fragment “zirconium dichloride” is replaced by

zirconium monochloride mono(2,4-di-tert-butylphenoxide)

zirconium monochloride mono(2,6-di-tert-butylphenoxide)

zirconium monochloride mono(3,5-di-tert-butylphenoxide)

zirconium monochloride mono(2,6-di-sec-butylphenoxide)

zirconium monochloride mono(2,4-di-methylphenoxide)

zirconium monochloride mono(2,3-di-methylphenoxide)

zirconium monochloride mono(2,5-di-methylphenoxide)

zirconium monochloride mono(2,6-di-methylphenoxide)

zirconium monochloride mono(3,4-di-methylphenoxide)

zirconium monochloride mono(3,5-di-methylphenoxide)

zirconium monochloride monophenoxide

zirconium monochloride mono(2-methylphenoxide)

zirconium monochloride mono(3-methylphenoxide)

zirconium monochloride mono(4-methylphenoxide)

zirconium monochloride mono(2-ethylphenoxide)

zirconium monochloride mono(3-ethylphenoxide)

zirconium monochloride mono(4-ethylphenoxide)

zirconium monochloride mono(2-sec-butylphenoxide)

zirconium monochloride mono(2-tert-butylphenoxide)

zirconium monochloride mono(3-tert-butylphenoxide)

zirconium monochloride mono(4-sec-butylphenoxide)

zirconium monochloride mono(4-tert-butylphenoxide)

zirconium monochloride mono(2-isopropyl-5-methylphenoxide)

zirconium monochloride mono(4-isopropyl-3-methylphenoxide)

zirconium monochloride mono(5-isopropyl-2-methylphenoxide)

zirconium monochloride mono(5-isopropyl-3-methylphenoxide)

zirconium monochloride mono(2,4-bis-(2-methyl-2-butyl)phenoxide)

zirconium monochloride mono(2,6-di-tert-butyl-4-methylphenoxide)

zirconium monochloride mono(4-nonylphenoxide)

zirconium monochloride mono(1-naphthoxide)

zirconium monochloride mono(2-naphthoxide)

zirconium monochloride mono(2-phenylphenoxide)

zirconium monochloride mono(tert-butoxide)

zirconium monochloride mono(N-methylanilide)

zirconium monochloride mono(2-tert-butylanilide)

zirconium monochloride mono(tert-butylamide)

zirconium monochloride mono(di-isopropylamide)

zirconium monochloride monomethyl

zirconium monochloride monobenzyl

zirconium monochloride mononeopentyl.

Preference is also given to the corresponding dimethylzirconiumcompounds and the corresponding η⁴-butadienezirconium compounds, andalso the corresponding compounds having 1,2-(1-methylethanediyl),1,2-(1,1-dimethylethanediyl) and 1,2(1,2-dimethylethanediyl) bridges.

The ratio of rac isomer to meso isomer of the metallocene component ofthe formula (A) in the catalyst system of the present invention is inthe range from 1:10 to 2:1, preferably from 1:2 to 3:2.

The methods of preparing metallocenes of the formula (A) are describedin detail in, for example, Journal of Organometallic Chem. 288 (1985)63-67 and in the documents cited therein.

The catalyst system of the present invention is obtainable by reactionof a Lewis base of the formula (I) and an organoboroaluminum compoundmade up of units of the formula (II) with a support. This is followed byreaction with a solution or suspension of one or more metallocenecompounds of the formula (VI) and, if desired, one or moreorganometallic compounds of the formula (V).

The activation of the catalyst system can be carried out either beforeintroduction into the reactor or else only in the reactor itself. Thepresent invention also provides a process for preparing polyolefins. Theaddition of a further chemical compound which is introduced as additivebefore the polymerization can also be advantageous.

To prepare the catalyst system of the present invention, the supportmaterial is suspended in an organic solvent. Suitable solvents arearomatic or aliphatic solvents, for example hexane, heptane, toluene orxylene, or halogenated hydrocarbons such as methylene chloride orhalogenated aromatic hydrocarbons such as o-dichlorobenzene. The supportcan be pretreated beforehand with a compound of the formula (V).Subsequently, one or more compounds of the formula (I) is/are added tothis suspension, with the reaction time being able to be from 1 minuteto 48 hours, preferably from 10 minutes to 2 hours. The reactionsolution can be isolated and subsequently resuspended or else can bereacted directly with a cocatalytically active organoboroaluminumcompound made up of units of the formula (II). The reaction time is from1 minute to 48 hours, preferably from 10 minutes to 2 hours. Preferenceis given to using from 1 to 4 equivalents of a Lewis base of the formula(I) per equivalent of a cocatalytically active compound made up of unitsof the formula (II). Particular preference is given to using oneequivalent of a Lewis base of the formula (I) per equivalent of acocatalytically active compound made up of units of the formula (II).The reaction product of this reaction is a metallocenium-formingcompound which is covalently bound to the support material. This willhereinafter be referred to as modified support material. The reactionmixture is subsequently filtered and the solid is washed with one of theabovementioned solvents. The modified support material is then dried ina high vacuum. After drying, the modified support material can beresuspended and after-treated with a compound of the formula (V).However, the compound of the formula (V) can also be added beforefiltration and drying of the modified support material.

The application of one or more metallocene compounds, preferably ones ofthe formula (A), and one or more organometallic compounds of the formula(V) to the modified support material is preferably carried out bydissolving or suspending one or more metallocene compounds of theformula (A) in one of the above-described solvents and subsequentlyreacting it with one or more compounds of the formula (V) which is/arelikewise in dissolved or suspended form. The stochiometric ratio ofmetallocene compound of the formula (A) to an organometallic compound ofthe formula (V) is from 100:1 to 10⁻⁴:1. The ratio is preferably from1:1 to 10⁻²:1. The modified support material can either be placeddirectly in the polymerization reactor or in a reaction flask in one ofthe abovementioned solvents. A mixture of a metallocene compound of theformula (A) and an organometallic compound of the formula (V) is thenadded. However, if desired, one or more metallocene compounds of theformula (A) can also be added to the modified support material without aprior addition of an organometallic compound of the formula (V).

The ratio of modified support to a metallocene compound of the formula(A) is preferably from 10 g:1 μmol to 10⁻² g:1 μmol. The stochiometricratio of metallocene compound of the formula (A) to the supportedcocatalytically active organoboroaluminum compound comprising units ofthe formula (II) is from 100:1 to 10⁻⁴:1, preferably from 1:1 to 10⁻²:1.

The supported catalyst system can be used directly for polymerization.However, it is also possible to remove the solvent and to resuspend thecatalyst system for use in the polymerization. The advantage of thisactivation method is that it offers the option of allowing thepolymerization-active catalyst system to be formed only in the reactoritself. This prevents partial decomposition from occurring duringintroduction of the air-sensitive catalyst.

The supported catalyst system prepared in this way can either be useddirectly for the polymerization of propylene or be prepolymerized usingone or more olefinic monomers before it is used in a polymerizationprocess. The prepolymerization procedure for supported catalyst systemsis described, for example, in WO 94/28034.

The present invention also provides a process for preparingpolypropylene by polymerization of propylene in the presence of thenovel catalyst system comprising at least one transition metal componentof the formula (A). For the purposes of the present invention, the termpolymerization encompasses both homopolymerization and copolymerization,but refers in particular to homopolymerization of propylene.

The polymerization is carried out at from −60 to 300° C., preferablyfrom 50 to 200° C., very particularly preferably 50−80° C. The pressureis from 0.5 to 2000 bar, preferably from 5 to 64 bar.

The polymerization can be carried out in solution, in bulk, insuspension or in the gas phase, continuously or batchwise, in one ormore stages.

The catalyst system of the present invention can be used as solecatalyst component for the polymerization of propylene, but ispreferably used in combination with at least one alkyl compound of anelement of main groups I to III of the Periodic Table, e.g. an aluminumalkyl, magnesium alkyl or lithium alkyl or an aluminoxane. The alkylcompound is added to the monomer or suspension medium and serves to freethe monomer of substances which can impair the catalyst activity. Theamount of alkyl compound added depends on the quality of the monomersused.

As molar mass regulator and/or to increase the activity, preference isgiven to adding hydrogen.

In addition, a mixture of a metal salt of Medialan acid, a metal salt ofanthranilic acid and a polyamine can be used as antistatic, as describedin EP-A-0,636,636.

Commercially available products such as Stadis® 450 from DuPont, namelya mixture of toluene, isopropanol, dodecylbenzenesulfonic acid, apolyamine, a copolymer of 1-decene and SO₂ and also 1-decene or ASA®-3from Shell and ARU5R® 163 from ICI can likewise be used.

The antistatic is preferably used as a solution; in the preferred caseof Stadis® 450, preference is given to using from 1 to 50% by weight ofthis solution, preferably from 5 to 25% by weight, based on the mass ofthe supported catalyst used (support together with covalently boundmetallocenium-forming compound and one or more metallocene compounds,e.g. of the formula A). The amounts of antistatic required may, however,vary within a wide range depending on the type of antistatic used.

The actual polymerization is preferably carried out in liquid monomer(bulk) or in the gas phase.

The antistatic can be introduced into the polymerization at any point intime. In an example of a preferred procedure, the supported catalystsystem is resuspended in an organic solvent, preferably alkanes such asheptane or isododecane. It is subsequently introduced into thepolymerization autoclave while stirring. The antistatic is then meteredin. The polymerization is carried out at from 0 to 100° C. In a furtherpreferred procedure, the antistatic is introduced into thepolymerization autoclave before addition of the supported catalystsystem. The resuspended supported catalyst system is subsequentlyintroduced while stirring at from 0 to 100° C. The polymerization timecan be in the range from 0.1 to 24 hours. Preference is given to apolymerization time in the range from 0.1 to 5 hours.

The polypropylenes prepared using the catalyst system of the presentinvention display a uniform particle morphology and contain no fines. Nodeposits or caked material occur in the polymerization using thecatalyst system of the present invention.

The catalyst system of the present invention gives polypropylenes havingextraordinarily high stereospecificity and regiospecificity.

Particular measures of the stereospecificity and regiospecificity ofpolypropylene are the triad tacticity (TT) and the proportion of2-1-inserted propene units (RI), both of which can be determined fromthe ¹³C-NMR spectra.

The ¹³C-NMR spectra are measured in a mixture of hexachlorobutadiene andd₂-tetrachloroethane at elevated temperature (365 K). All ¹³C-NMRspectra of the polypropylene samples measured are calibrated on thebasis of the resonance signal of d₂-tetrachloroethane (δ=73.81 ppm).

To determine the triad tacticity of polypropylene, the methyl resonancesignals in the ¹³C-NMR spectrum in the range from 23 to 16 ppm areexamined; cf. J. C. Randall, Polymer Sequence Determination: Carbon-13NMR Method, Academic Press New York 1978; A. Zambelli, P. Locatelli, G.Bajo, F. A. Bovey, Macromolecules 8 (1975), 687-689; H. N. Cheng, J. A.Ewen, Makromol. Chem. 190 (1989), 1931-1943. Three successive1-2-inserted propene units whose methyl groups are located on the sameside in the “Fischer projection” are referred to as mm triads (δ=21.0ppm to 22.0 ppm). If only the second methyl group of the threesuccessive propene units points to the other side, one speaks of an rrtriad (δ=19.5 ppm to 20.3 ppm), and if only the third methyl group ofthe three successive propene units points to the other side, one speaksof an mr triad (δ=20.3 ppm to 21.0 ppm). The triad tacticity iscalculated according to the following formula:

TT(%)=mm/(mm+mr+rr)×100

If one propene unit is inserted inversely into the growing polymerchain, this is referred to as a 2-1-insertion; cf. T. Tsutsui, N.Ishimaru, A. Mizuno, A. Toyota, N. Kashiwa, Polymer 30, (1989), 1350-56.The following different structural arrangements are possible:

The proportion of 2-1-inserted propene units (RI) can be calculatedaccording to the following formula:

RI(%)=0.5Iα,β(Iα,α+Iα,β+Iα,β)×100,

where

Iα,α is the sum of the intensities of the resonance signals at δ=41.84,42.92 and 46.22 ppm,

Iα,β is the sum of the intensities of the resonance signals at δ=30.13,32.12, 35.11 and 35.57 ppm and

Iα,δ is the intensity of the resonance signal at δ=37.08 ppm.

The isotactic polypropylene which has been prepared using the catalystsystem of the present invention has a proportion of 2-1-inserted propeneunits RI of <0.5% at a triad tacticity TT of >98.0% and a melting pointof >153° C.; M_(w)/M_(n), of the polypropylene prepared according to thepresent invention is in the range from 2.5 to 3.5.

The propylene copolymers which can be prepared using the catalyst systemof the present invention have a significantly higher molar mass thanthose of the prior art. At the same time, such copolymers can beprepared with high productivity at industrially relevant processparameters without deposit formation by use of the catalyst system ofthe present invention.

The polypropylene prepared by the process of the present invention isparticularly suitable for producing hard and stiff shaped bodies havinga high tensile strength, e.g. fibers, filaments, injection-molded parts,films, sheets or large hollow bodies (e.g. pipes).

The following examples illustrate the invention but do not restrict itsscope.

General information: preparation and handling of the compounds werecarried out with exclusion of air and moisture under argon (Schlenktechnique). All solvents required were dried before use by boiling for anumber of hours over suitable desiccants and subsequent distillationunder argon.

EXAMPLE 1 Synthesis of bis(pentafluorophenylboroxy)methylalane

5 ml of trimethylaluminum (2M in toluene, 10 mmol) together with 45 mlof toluene are placed in a reaction vessel. At −40° C., 6.92 g ofpentafluoroboronic acid (20 mmol) in 50 ml of toluene are added dropwiseto this solution over a period of 15 minutes. The mixture is stirred for1 hour at −40° C. and subsequently for another hour at room temperature.The turbid solution is filtered through a G4 frit. This gives a clear,colorless solution (0.1M based on Al) ofbis(pentafluorophenylboroxy)methylalane in toluene.

EXAMPLE 2 Application of bis(pentafluorophenylboroxy)methylalane to aSupport

2 g of SiO2 (PQ MS3030, pretreated at 140° C., 10 mbar, 10 hours) aresuspended in 30 ml of toluene, and 0.5 ml of N,N-dimethylaniline isadded at room temperature. The mixture is cooled to 0° C. and addeddropwise from a dropping funnel to 40 ml of the solution prepared inExample 1. The mixture is allowed to warm to room temperature and isstirred for another 3 hours. The suspension is subsequently filtered andthe solid is washed with pentane. The residue is then dried to constantweight in an oil pump vacuum. This gives 4.01 g of a pale purple supportmaterial.

EXAMPLE 3 Preparation of Catalyst System 1

0.013 ml of trimethylaluminum (2M in toluene, 25 μmol) is added to 3.9mg ofdimethylsilanediylbis(2-n-propyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride (rac/meso ratio=1:1.5 μmol) in 3 ml of toluene and themixture is stirred for 6 hours. Subsequently, 0.24 g of the supportprepared in Example 2 is added at room temperature. The catalystsuspension is stirred for 1 hour and the solvent is then taken off in anoil pump vacuum. This gives a pink, free-flowing powder.

EXAMPLE 4 Polymerization Using Catalyst System 1

A dry 2 l reactor is flushed firstly with nitrogen and subsequently withpropylene and charged with 1.5 l of liquid propylene. 3 ml of TIBA (20%strength in Varsol) are added thereto and the mixture is stirred for 15minutes. The catalyst system 1 prepared in Example 3 resuspended in 20ml of heptane is subsequently injected and rinsed in with 15 ml ofheptane. The reaction mixture is heated to the polymerizationtemperature of 60° C. and polymerized for one hour. The polymerizationis stopped by venting the remaining propylene. The polymer is dried in avacuum drying oven. This gives 630 g of polypropylene powder. Thereactor displays no deposits on the interior wall or stirrer. Thecatalyst activity is 161 kg of PP/g of metallocene×h.

EXAMPLE 5 Preparation of Catalyst System 2

0.013 ml of trimethylaluminum (2M in toluene, 25 μmol) is added to 3.9mg ofdimethylsilanediylbis(2-ethyl(4′-tert-butylphenyl)indenyl)zirconiumdichloride (rac/meso ratio=1:1.5 μmol) in 3 ml of toluene and themixture is stirred for 4 hours. Subsequently, 0.24 g of the supportprepared in Example 2 is added at room temperature. The catalystsuspension is stirred for 1 hour and the solvent is then taken off in anoil pump vacuum. This gives a pink, free-flowing powder.

EXAMPLE 6 Polymerization Using Catalyst System 2

A dry 2 l reactor is flushed firstly with nitrogen and subsequently withpropylene and charged with 1.5 l of liquid propylene. 3 ml of TIBA (20%strength in Varsol) are added thereto and the mixture is stirred for 15minutes. The catalyst system 2 prepared in Example 5 resuspended in 20ml of heptane is subsequently injected and rinsed in with 15 ml ofheptane. The reaction mixture is heated to the polymerizationtemperature of 60° C. and polymerized for one hour. The polymerizationis stopped by venting the remaining propylene. The polymer is dried in avacuum drying oven. This gives 595 g of polypropylene powder. Thereactor displays no deposits on the interior wall or stirrer. Thecatalyst activity is 153 kg of PP/g of metallocene×h.

EXAMPLE 7 Preparation of Catalyst System 3

0.02 ml of trimethylaluminum (2M in toluene, 40 μmol) is added to 3,1 mgof dimethylsilanediylbis(2-methyl-4-phenylindenyl)zirconium dichloride(100% rac; 5 μmol) in 3 ml of toluene and the mixture is stirred for 1hour. 0.48 g of the support prepared in Example 2 is subsequently addedat room temperature. The catalyst suspension is stirred for 1 hour andthe solvent is then taken off in an oil pump vacuum. This gives a pink,free-flowing powder.

EXAMPLE 8 Comparative Polymerization Using Catalyst System 3

A dry 2 l reactor is flushed firstly with nitrogen and subsequently withpropylene and charged with 1.5 l of liquid propylene. 3 ml of TIBA (20%strength in Varsol) are added thereto and the mixture is stirred for 15minutes. The catalyst system 3 prepared in Example 7 resuspended in 20ml of heptane is subsequently injected and rinsed in with 15 ml ofheptane. The reaction mixture is heated to the polymerizationtemperature of 60° C. and polymerized for one hour. The polymerizationis stopped by venting the remaining propylene. The polymer is dried in avacuum drying oven. This gives 320 g of polypropylene powder. Thereactor displays no deposits on the interior wall or stirrer. Thecatalyst activity is 103 kg of PP/g of metallocene×h.

EXAMPLE 9 Polymerization Using Catalyst System 2 in the Presence ofHydrogen

A dry 2 l reactor is flushed first with nitrogen and subsequently withpropylene. 0.3 bar of hydrogen are subsequently introduced into thereactor. The reactor is then charged with 1.5 l of liquid propylene. 3ml of TIBA (20% strength in Varsol) are added thereto and the mixture isstirred for 15 minutes. Subsequently, half of the catalyst system 2prepared as described in Example 5[=1.95 mg ofdimethylsilanediylbis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)zirconiumdichloride (rac/meso 1:1; 2.5 μmol) resuspended in 20 ml of heptane isinjected and rinsed in with 15 ml of heptane. The reaction mixture isheated to the polymerization temperature of 60° C. and polymerization iscarried out for one hour. The polymerization is stopped by venting theremaining propylene. The polymer is dried in a vacuum drying oven. Thisgives 620 g of polypropylene powder. The reactor displays no deposits onthe interior wall or stirrer. The catalyst activity is 318 kg of PP/g ofmetallocene×h.

The polymerization results from the examples are shown in Table 1.

TABLE I Content of rac Yield [kg of Activity [kg of m.p. Examplerac/meso form PP] PP/g of met/h] [° C.] 4 1:1 50% 0.630 161 157 6 1:150% 0.595 153 154 8 rac 100% 0.640 103 150 9 1:1 50% 0.620 318 157

We claim:
 1. A catalyst system comprising a) at least one substitutedmetallocene of formula (A)

 where R¹ and R² are identical or different and each represents ahydrogen atom, or a C₁-C₂₀-hydrocarbon group, with the proviso that R¹is not methyl when R² is hydrogen, M¹ is a transition metal of group 4,5 or 6 of the Periodic Table of the Elements, A is a bridge of formula

 or is ═BR³, ═AlR³, —S—, ═SO, ═SO₂, ═NR³, ═PR³, ═P(O)R³, o-phenylene or2,2′-biphenylene, where M² is carbon, silicon, germanium or tin, o is 1,2, 3 or 4, R³ and R⁴ are identical or different and each represents ahydrogen atom, halogen, C₁-C₂₀-alkyl, C₆-C₁₄-aryl, C₁-C₁₀-alkoxy,C₂-C₁₀-alkenyl, C₇-C₂₀-arylalkyl, C₇-C₂₀-alkylaryl, C₆-C₁₀-aryloxy,C₁-C₁₀-fluoroalkyl, C₆-C₁₀-haloaryl, C₂-C₁₀-alkynyl, C₃-C₂₀-alkylsilyl,C₆-C₂₀-arylsilyl or C₇-C₂₀-alkylarylsilyl, or R³ and R⁴ together form amonocyclic or polycyclic ring system, and X are identical or differentand each X represents a hydrogen atom, a halogen atom, a hydroxyl group,a C₁-C₁₀-alkyl group, a C₆-C₁₅-aryl group, a C₁-C₁₀-alkoxy group, aC₆-C₁₅-aryloxyl group, a benzyl group or an NR⁵ ₂ group, where R⁵ areidentical or different and each R⁵ represents a fluorine atom, achlorine atom, a C₁-C₁₀-alkyl group, a C₆-C₁₅-aryl group or a (CH₃)₃Sigroup, where the ratio of rac isomer to meso isomer of the metalloceneof formula (A) is from 1:10 to 2:1, b) at least one Lewis base offormula (I), M³R⁶R⁷R⁸  (I)  where R⁶, R⁷ and R⁸ are identical ordifferent and each represents a hydrogen atom, a C₁-C₂₀-alkyl group, aC₁-C₂₀-haloalkyl group, a C₆-C₄₀-aryl group, a C₆-C₄₀-haloaryl group, aC₇-C₄₀-alkylaryl group or a C₇-C₄₀-arylalkyl group, where two radicalsor all three radicals R⁶, R⁷ and R⁸ are optionally joined to one anothervia C₂-C₂₀ units, and M³ is an element of main group V of the PeriodicTable of the Elements, c) a support, d) at least one organoboroaluminumcompound which is covalently bound to the support, and which is made upof units of formula (II) R_(i) ⁹M⁴—O—M⁴R_(j) ¹⁰  (II)  where R⁹ and R¹⁰are identical or different and each represents a hydrogen atom, ahalogen atom, C₁-C₂₀-alkyl, C₁-C₂₀-haloalkyl, C₁-C₁₀-alkoxy,C₆-C₂₀-aryl, C₆-C₂₀-haloaryl, C₆-C₂₀-aryloxy, C₇-C₄₀-arylalkyl,C₇-C₄₀-haloarylalkyl, C₇-C₄₀-alkylaryl or C₇-C₄₀-haloalkylaryl, or R⁹ isan —OSiR₃ group, where R are identical or different and each R is asdefined for R⁹, M⁴ are identical or different and each M⁴ represents anelement of main group 3 of the Periodic Table of the Elements, and i andj are each an integer 1 or 2, and optionally e) an organometalliccompound of formula (V) [M⁵R¹¹ _(p)]_(k)  (V)  where M⁵ is an element ofmain group I, II or III of the Periodic Table of the Elements, R¹¹ areidentical or different and each R¹¹ represents a hydrogen atom, ahalogen atom, a C₁-C₂₀-alkyl group, a C₆-C₄₀-aryl group, aC₇-C₄₀-arylalkyl group or a C₇-C₄₀-alkylaryl group, p is an integer from1 to 3, and k is an integer from 1 to
 4. 2. A catalyst system as claimedin claim 1, wherein R¹ and R² are identical or different and eachrepresents a hydrogen atom, a C₁-C₂₀-alkyl group, a C₆-C₁₄-aryl group ora C₂-C₂₀-alkenyl group, with the proviso that R¹ is not methyl when R²is hydrogen, M¹ is titanium, zirconium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum or tungsten, A is dimethylsilanediyl,dimethylgermanediyl, ethylidene, methylethylidene,1,1-dimethylethylidene, 1,2-dimethylethylidene, tetramethylethylidene,isopropylidene, phenylmethylmethylidene or diphenylmethylidene, X areidentical or different and each X represents a hydrogen atom, fluorine,chlorine, bromine, iodine, a hydroxyl group, methyl, ethyl, propyl,isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, hexyl, cyclohexyl,phenyl, naphthyl, methoxy, ethoxy, tert-butoxy or an NR⁵ ₂ group, whereR⁵ are identical or different and each R⁵ represents methyl, ethyl, achlorine atom or a fluorine atom, where the ratio of rac isomer to mesoisomer of the metallocene of formula (A) is from 1:2 to 3:2.
 3. Acatalyst system as claimed in claim 1, wherein R¹ and R² are identicalor different and each represents hydrogen, methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl or hexyl,with the proviso that R¹ is not methyl when R² is hydrogen, M¹ iszirconium, A is dimethylsilanediyl, dimethylgermanediyl or ethylidene, Xare identical or different and each X represents hydrogen, fluorine,chlorine, bromine, a hydroxyl group, methyl, ethyl, propyl, isopropyl,n-butyl, isobutyl, sec-butyl, tert-butyl, hexyl, cyclohexyl, phenyl,naphthyl, methoxy, ethoxy or tert-butoxy, where the ratio of rac isomerto meso isomer of the metallocene of formula (A) is from 1:2 to 3:2. 4.A catalyst system as claimed in claim 1, wherein R⁹ and R¹⁰ in formula(II) are C₁-C₂₀-alkyl, C₁-C₂₀-haloalkyl, C₁-C₁₀-alkoxy, C₆-C₂₀-aryl,C₆-C₂₀-haloaryl, C₆-C₂₀-aryloxy, C₇-C₄₀-arylalkyl, C₇-C₄₀-haloarylalkyl,C₇-C₄₀-alkylaryl or C₇-C₄₀-haloalkylaryl.
 5. A catalyst system asclaimed in in claim 1, wherein R¹¹ in formula (V) is C₁-C₂₀alkyl,C₆-C₄₀-aryl, C₇-C₄₀-arylalkyl or C₇-C₄₀-alkylaryl.
 6. A catalyst systemas claimed in claim 1, wherein the support used is an organic orinorganic, inert solid.
 7. A process for preparing polyolefins bypolymerization of propylene in the presence of a catalyst system asclaimed in claim
 1. 8. A process as claimed in claim 7, wherein thepolymerization of propylene is carried out in the additional presence ofhydrogen.